Monte Carlo Structure Simulations for Aqueous 1,4-Dioxane Solutions

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• 作者：Peter I. Nagy ; Gergely V&ouml ; lgyi ; Krisztina Tak&aacute ; cs-Nov&aacute ; k
• 刊名：Journal of Physical Chemistry B
• 出版年：2008
• 出版时间：February 21, 2008
• 年：2008
• 卷：112
• 期：7
• 页码：2085 - 2094
• 全文大小：203K
• 年卷期：v.112,no.7(February 21, 2008)
• ISSN：1520-5207

文摘

Monte Carlo simulations in the NpT ensembles have been performed for the structure exploration of aqueous1,4-dioxane solutions. Three different systems with all-atom dioxane:TIP4P water molar compositions of2:500 (code:D2), 8:465 (D8), and 17:425 (D17) modeled solutions of 0.22, 0.88, and 1.86 mol/dm³concentrations, respectively, at T = 298 K and p = 1 atm. The calculated solution densities increase from0.992 to 1.002 g/cm³ with increasing dioxane concentration and approach the experimentally determineddensities within 1%. This close agreement was achieved by utilizing RESP charges fitted to the in-solutionIEF-PCM/B3LYP/6-31G* electrostatic potential of dioxane taken in its chair conformation and recentlydeveloped C, H steric parameters for ethers for calculations with a 12-6-1 all-atom potential. Solution structureanalyses pointed out that the dioxane molecules arrange in the solutions with favorable distances of 4-8 Åfor the ring symmetry centers. Within this range not only pairs of rings but triangular triads and tetrads havealso been observed with center-center distances <8 Å. For the D8 system, about 25% of the sampledconfigurations included such a triad. In the case of the D17 model, two simulations starting from differentsolution configuration predicted different degrees for the dioxane aggregation in aqueous solution. In themore aggregated structure 3-21 triads are consistently maintained and 1-2 tetrads are formed in 58% of theconfigurations. Each dioxane oxygen forms about one hydrogen bond, on average, to a water molecule in the0.22-1.86 molar range. The most likely O(dioxane)···H(water) hydrogen bond distance is 1.75-1.80 Åcompared to the optimal distance of 1.72 Å in the isolated dimer. The optimal dioxane-water interactionenergy of -5.65 kcal/mol indicates a remarkable hydrogen-bond acceptor character for dioxane.